1. Field of the Invention
The present invention relates to a magnetoresistance element, and to a thin-film magnetic head, a head assembly and a magnetic recording drive each including the magnetoresistance element.
2. Description of the Related Art
With recent improvements in recording density of magnetic recording devices such as magnetic disk drives, there has been a demand for improving the performance of thin-film magnetic heads. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has a structure in which a read head unit including a magnetoresistance element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. Each thin-film magnetic head has a medium facing surface to face a recording medium.
An example of MR elements that can achieve high sensitivity and high output is a TMR element which uses the tunneling magnetoresistance effect. The TMR element typically includes a free layer, a pinned layer, a tunnel barrier layer located between the free layer and the pinned layer, and an antiferromagnetic layer located on a side of the pinned layer opposite from the tunnel barrier layer. The free layer is a ferromagnetic layer whose magnetization direction changes in response to a signal magnetic field. The pinned layer is a ferromagnetic layer whose magnetization direction is pinned. The antiferromagnetic layer is to pin the magnetization direction of the pinned layer by means of exchange coupling with the pinned layer. The tunnel barrier layer is typically formed of an insulating material such as aluminum oxide (Al2O3) or magnesium oxide (MgO).
Now, an example of the configuration of a read head unit incorporating a TMR element will be described. The read head unit includes a first electrode, a second electrode, and a TMR element. The TMR element is located near the medium facing surface and detects a signal magnetic field from a recording medium. The first and second electrodes are located on opposite sides of the TMR element in the direction in which a plurality of layers constituting the TMR element are stacked. The first and second electrodes feed the TMR element a sense current for detecting a signal corresponding to the signal magnetic field. The sense current flows in a direction intersecting the plane of the layers constituting the TMR element, such as a direction perpendicular to the plane of the layers constituting the TMR element.
The TMR element includes a stack including the free layer, the tunnel barrier layer, the pinned layer and the antiferromagnetic layer mentioned above. The stack has a front end face located in the medium facing surface, a rear end face located opposite to the front end face, and first and second sidewalls located at opposite ends of the stack in the track width direction. The TMR element further includes a first insulating layer in contact with the first sidewall, and a second insulating layer in contact with the second sidewall.
The read head unit further includes first and second bias magnetic field applying layers located on opposite sides of the stack in the track width direction. At least part of the first insulating layer is interposed between the first sidewall and the first bias magnetic field applying layer. At least part of the second insulating layer is interposed between the second sidewall and the second bias magnetic field applying layer. The read head unit further includes an insulating refill layer provided around the stack, the first and second insulating layers and the first and second bias magnetic field applying layers.
The first and second bias magnetic field applying layers apply to the TMR element a bias magnetic field for orienting the magnetization of the free layer in a predetermined direction when no signal magnetic field is applied to the TMR element.
The read head unit having the above-described configuration is disclosed in, for example, U.S. Pat. No. 9,030,784 B2.
An example of a manufacturing method for the read head unit will now be described. The manufacturing method starts with forming on the first electrode a layered film that later becomes the aforementioned stack. The layered film is composed of a plurality of layers stacked on each other. Then, the layered film is etched using a first mask to thereby provide the layered film with the aforementioned first and second sidewalls. Next, the first and second insulating films and the first and second bias magnetic field applying layers are formed in succession, and the first mask is removed. The layered film is then etched using a second mask to thereby provide the layered film with the aforementioned rear end face. The layered film thereby becomes an initial stack. The initial stack has the first and second sidewalls and the rear end face, but does not have the front end face yet. Next, the insulating refill layer is formed and the second mask is removed. The second electrode is then formed on the initial stack. A manufacturing method for a magnetic head including the read head unit includes the step of forming the medium facing surface. In the step of forming the medium facing surface, the initial stack is provided with the front end face and thereby becomes the aforementioned stack.
According to the manufacturing method for the read head unit described above, during the step of etching the layered film to form the first and second sidewalls, flying substances generated by the etching of the layered film may adhere to the first and second sidewalls to form an adhesion film on each of the first and second sidewalls. If the adhesion film is formed of metal, the free layer and the pinned layer can be short-circuited via the adhesion film. If the free layer and the pinned layer are short-circuited via the adhesion film, there arises the problem of a reduction in the magnetoresistance change ratio of the TMR element.
It is difficult to completely eliminate the adhesion film by adjusting the etching conditions in the step of etching the layered film to form the first and second sidewalls.
In order to prevent the free layer and the pinned layer from being short-circuited via the adhesion film, U.S. Pat. No. 8,828,742 B2 discloses the technique to form an insulating metal oxide layer by oxidizing the adhesion film of metal formed on the first and second sidewalls.
In the process of manufacturing a magnetic head, a step following the formation of the initial stack, such as the step of fabricating an induction-type electromagnetic transducer, may include heat treatment at temperatures of around 200° C. to 300° C. Suppose that the adhesion film of metal formed on the first and second sidewalls is oxidized to form a metal oxide layer in the step of forming the initial stack. In such a case, if the foregoing heat treatment is performed after the formation of the initial stack, the metal oxide layer can undergo a reduction reaction and change into a metal layer. This gives rise to the problem that the free layer and the pinned layer are short-circuited via the metal layer to reduce the magnetoresistance change ratio of the TMR element.